I have a pair of hearing aids which can be toggled between listening modes (telephone, noisy room, outdoors, etc.) using a key fob-like device. The control fob was lost before I got the aids, so I could not take it apart for study. However, each of the hearing aids has a pushbutton on it which lets you manually toggle the modes- and as if by magic, when you toggle one of the aids, the other one wirelessly switches modes as well so both aids are always operating in the same mode.
Does anyone know what frequencies are allocated for this application? Unfortunately I do not have an RF signal analyzer with which I could tune in to the aids while they are signaling each other to switch modes.